Friction materials such as disc brake pads, brake lining or the like are used for the purpose of braking of the automobiles and the like. Such a friction material plays the role of braking by being rubbed against an opposite material, for example, a disc rotor or a brake drum, for braking. Therefore, the friction materials are not only required to have a high friction coefficient and stability in the friction coefficient, but also required to have characterristics that the friction material does not easily shave a disc rotor which is a facing material (rotor wear), brake squeal does not easily occur (brake squeal characteristics), and the pad service life is long (pad service life).
Furthermore, in recent years, friction materials are required to have a less decrease in the friction coefficient (fast fading characteristics), even under severe braking conditions such that the braking temperature abnormally rises due to continuous high speed braking (a vehicle speed of 200 km/h or higher) or high deceleration braking (0.8 G or higher).
However, friction materials include a Low Steel material (hereinafter, also referred to as “LS material”) which contains steel fiber as a fibrous base material and hard abrasive particles as an abrasive material, and a Non-Asbest Organic material (hereinafter, also referred to as “NAO material”) which does not contain steel fiber and contains almost no hard abrasive particles.
The former has excellent fast fading characteristics but has inferior rotor wear and inferior brake squeal characteristics. The latter has excellent rotor wear and excellent brake squeal characteristics, but has inferior fast fading characteristics. Furthermore, NAO materials cause large pad wear amounts during fast fading and frequently cause uneven wear of the pad as compared with the LS materials.
Heretofore, attempts have been made to improve in the fading characteristics of NAO materials, and for example, it has been reported to achieve an improvement by using a large amount of vulcanized rubber powder instead of cashew dust and by increasing the thermal conductivity (see, for example, Patent Document 1), while it has been reported to achieve an improvement through the addition of activated alumina and a fluoropolymer (see, for example, Patent Document 2). However, the effect of improving the fading characteristics in the high-speed range (a vehicle speed of 200 km/h or higher) as described above, is not sufficient as compared with the characteristics of the LS materials.